Buy Nothing groups offer an antidote to waste and isolation (washingtonpost.com)

Same. People are usually a lot less flaky than on Craigslist's free section. Like, if they say they're coming to get the item, they usually do.

For local activities tied to IRL interactions, a key benefit of FB groups is the lack of anonymity - easier to block people and alert the group to scams or other malicious activity. It's not perfect and there are still ways to subvert policies, but it seems to work in practice. I wish there were other popular options for explicitly-not-anonymous social media, perhaps we'll see some eventually.